The present invention relates to an electric power steering apparatus in which a motor current instruction value representative of the value of the current to flow through a motor is determined based on the steering torque detected by a torque sensor and the motor is driven in accordance with the determined motor current instruction value.
An electric power steering apparatus mounted on a vehicle assists the steering power of the vehicle with a motor, and is structured so that a steering mechanism to which the steering wheel is coupled through a steering shaft is provided with a torque sensor that detects the steering torque applied to the steering wheel and a motor that assists the operation of the steering mechanism and the motor is driven in accordance with the steering torque detected by the torque sensor to thereby reduce the operation force on the steering wheel.
In a case where the steering assisting motor used in an electric power steering apparatus is, for example, a brushless motor, the brushless motor has a characteristic such that although the number of rotation increases as the applied voltage increases, the maximum value of the rotation torque determined based on the current flow is the same irrespective of the voltage as shown in FIG. 1, and therefore, the higher the applied voltage is, the faster the motor can rotate at the same rotation torque.
The steering assisting motor is driven by a mounted battery, and fluctuations in the voltage of the mounted battery are assumed to be, for example, 10 to 16 V. The steering assisting motor, which is designed so as to suit the assumed minimum voltage (10 V) in consideration of the fluctuations in the voltage of the mounted battery, is a low-voltage and large-current motor, and has a size larger than a motor designed for a higher voltage.
The present invention is made in view of the above-described circumstances, and an object thereof is to provide an electric power steering apparatus in which a voltage from which a stable steering assisting force is always obtained can be supplied to the steering assisting motor even when the voltage of the mounted battery fluctuates, and the steering assisting motor can be reduced in size.
An electric power steering apparatus according to a first invention is provided with: a torque sensor for detecting a steering torque applied to a steering wheel; and a steering assisting motor driven by a drive circuit to which a voltage of a mounted battery is applied, in which a motor current instruction value representative of a value of current to flow through the motor is determined based on the steering torque detected by the torque sensor, the drive circuit rotates the motor in accordance with the determined motor current instruction value, and a steering power is assisted by a rotation torque outputted by the motor, is characterized by comprising: judging means for judging whether the motor current instruction value is higher than a first threshold value or not; boosting instruction outputting means for, when the judging means judges that the motor current instruction value is higher, outputting a boosting instruction for boosting the voltage of the mounted battery; and a boosting circuit for boosting the voltage of the mounted battery in response to the boosting instruction outputted by the boosting instruction outputting means, wherein the voltage boosted by the boosting circuit is applied to the drive circuit.
In this electric power steering apparatus of the first invention, the torque sensor detects the steering torque applied to the steering wheel, and the steering assisting motor is driven by the drive circuit to which the voltage of the mounted battery is applied. The motor current instruction value representative of the value of the current to be flown through the motor is determined based on the steering torque detected by the torque sensor, and the drive circuit rotates the motor based on the determined motor current instruction value. The judging means judges whether the motor current instruction value is higher than the first threshold value or not, and when the judging means judges that the motor current instruction value is higher, the boosting instruction outputting means outputs the boosting instruction for boosting the voltage of the mounted battery. The boosting circuit boosts the voltage of the mounted battery in response to the boosting instruction outputted by the boosting instruction outputting means, and the voltage boosted by the boosting circuit is applied to the drive circuit.
According to this structure, a voltage from which a stable steering assisting force is always obtained can be supplied to the steering assisting motor even when the voltage of the mounted battery falls, so that an electric power steering apparatus in which the steering assisting motor has a reduced size is realized.
An electric power steering apparatus according to a second invention is characterized by further comprising in addition to the first invention: judging means for judging whether or not the motor current instruction value is lower than a second threshold value that is lower than the first threshold value during the boosting circuit boosts the voltage of the mounted battery; and stepping down instruction outputting means for, when the judging means judges that the motor current instruction value is lower, outputting a stepping down instruction for stepping down the voltage, wherein the boosting circuit stops the boosting of the voltage of the mounted battery in response to the stepping down instruction outputted by the stepping down instruction outputting means.
In this electric power steering apparatus of the second invention, during the boosting circuit boosts the voltage of the mounted battery, the judging means judges whether or not the motor current instruction value is lower than the second threshold value that is lower than the first threshold value. When the judging means judges that the motor current instruction value is lower, the stepping down instruction outputting means outputs the stepping down instruction for stepping down the voltage. The boosting circuit stops the boosting in response to the outputted stepping down instruction. According to this structure, when it becomes unnecessary to boost the voltage of the mounted battery applied to the drive circuit, the voltage can be stepped down, and when a large steering assisting force becomes unnecessary, the voltage of the mounted battery can be supplied to the steering assisting motor without boosted, so that an electric power steering apparatus is realized in which the efficiency of the steering assisting motor can be prevented from being reduced by the boosting of the voltage of the mounted battery.
An electric power steering apparatus according to a third invention is characterized by, in addition to the first invention, further comprising calculating means for calculating the rotation torque when the judging means judges that the motor current instruction value is higher; wherein the boosting instruction outputting means outputs a boosting instruction for boosting the voltage of the mounted battery to a predetermined voltage in accordance with the rotation torque calculated by the calculating means.
In this electric power steering apparatus of the third invention, the torque sensor detects the steering torque applied to the steering wheel, and the steering assisting motor is driven by the drive circuit to which the voltage of the mounted battery is applied. The motor current instruction value representative of the value of the current to be flown through the motor is determined based on the steering torque detected by the torque sensor, the drive circuit rotates the motor based on the determined motor current instruction value, and the steering power is assisted by the rotation torque outputted by the motor. The judging means judges whether the motor current instruction value is higher than the first threshold value or not, and when the judging means judges that the motor current instruction value is higher, the calculating means calculates the rotation torque. The boosting instruction outputting means outputs the boosting instruction for boosting the voltage of the mounted battery to the predetermined voltage in accordance with the rotation torque calculated by the calculating means, and the boosting circuit boosts the voltage of the mounted battery to the predetermined voltage in response to the boosting instruction outputted by the boosting instruction outputting means. The predetermined voltage boosted by the boosting circuit is applied to the drive circuit.
According to this structure, the voltage of the mounted battery can be boosted in accordance with the rotation torque of the motor when the motor current instruction value is maximum, and a voltage from which a stable steering assisting force is always obtained can be supplied to the steering assisting motor even when the voltage of the mounted battery falls, so that an electric power steering apparatus in which the steering assisting motor has a reduced size is realized.
An electric power steering apparatus according to a fourth invention is characterized by, in addition to the first invention, further comprising calculating means for, when the judging means judges that the motor current instruction value is higher, calculating a ratio of the rotation torque to a maximum rotation torque that can be outputted by the motor; wherein the boosting instruction outputting means outputs a boosting instruction for boosting the voltage of the mounted battery to a predetermined voltage in accordance with the ratio calculated by the calculating.
In this electric power steering apparatus of the fourth invention, the torque sensor detects the steering torque applied to the steering wheel, and the steering assisting motor is driven by the drive circuit to which the voltage of the mounted battery is applied. The motor current instruction value representative of the value of the current to be flown through the motor is determined based on the steering torque detected by the torque sensor, the drive circuit rotates the motor based on the determined motor current instruction value, and the steering power is assisted by the rotation torque outputted by the motor. The judging means judges whether the motor current instruction value is higher than the first threshold value or not, and when the judging means judges that the motor current instruction value is higher, the calculating means calculates the ratio of the rotation torque to the maximum rotation torque that can be outputted by the motor. The boosting instruction outputting means outputs the boosting instruction for boosting the voltage of the mounted battery to the predetermined voltage in accordance with the ratio calculated by the calculating means, and the boosting circuit boosts the voltage of the mounted battery to the predetermined voltage in response to the boosting instruction outputted by the outputting means. The predetermined voltage boosted by the boosting circuit is applied to the drive circuit.
According to this structure, the voltage of the mounted battery can be boosted in accordance with the rotation torque of the motor when the motor current instruction value is maximum, and a voltage from which a stable steering assisting force is always obtained can be supplied to the steering assisting motor even when the voltage of the mounted battery falls, so that an electric power steering apparatus in which the steering assisting motor has a reduced size is realized.
An electric power steering apparatus according to a fifth invention is characterized by further comprising in addition to the third or fourth invention: judging means for judging whether or not the motor current instruction value is lower than a second threshold value that is lower than the first threshold value during the boosting circuit boosts the voltage of the mounted battery to the predetermined voltage; and stepping down instruction outputting means for, when the judging means judges that the motor current instruction value is lower, outputting a stepping down instruction for stepping down the voltage, wherein the boosting circuit stops the boosting of the voltage of the mounted battery to the predetermined voltage in response to the stepping down instruction outputted by the stepping down instruction outputting means.
In the electric power steering apparatus according to the fifth invention, the judging means judges whether the motor current instruction value is lower than the predetermined value or not during the boosting circuit boosts the voltage of the mounted battery to the predetermined voltage, and the stepping down instruction outputting means outputs the stepping down instruction for stepping down the voltage when the judging means judges that the motor current instruction value is lower. The boosting circuit stops the boosting of the voltage of the mounted battery to the predetermined voltage in response to the stepping down instruction outputted by the stepping down instruction outputting means.
According to this structure, when it becomes unnecessary to boost the voltage of the mounted battery applied to the drive circuit, the boosted voltage of the mounted battery can be stepped down, and when a large steering assisting force becomes unnecessary, the voltage of the mounted battery can be supplied to the steering assisting motor without boosted, so that an electric power steering apparatus is realized in which the efficiency of the steering assisting motor can be prevented from being reduced by the boosting of the voltage of the mounted battery.
An electric power steering apparatus according to a sixth invention is provided with: a torque sensor for detecting a steering torque applied to a steering wheel; and a steering assisting motor driven by a drive circuit to which a voltage of a mounted battery is applied, in which a motor current instruction value representative of a value of a current to be flown through the motor is determined based on the steering torque detected by the torque sensor, the drive circuit rotates the motor in accordance with the determined motor current instruction value, and a steering power is assisted by a rotation torque outputted by the motor, is characterized by comprising: a rotation number detector for detecting a number of rotations of the motor; judging means for judging whether the number of rotations detected by the rotation number detector is higher than a first threshold value or not; boosting instruction outputting means for, when the judging means judges that the number of rotations is higher, outputting a boosting instruction for boosting the voltage of the mounted battery to a predetermined voltage in accordance with the number of rotations; and a boosting circuit for boosting the voltage of the mounted battery to the predetermined voltage in response to the boosting instruction outputted by the boosting instruction outputting means, wherein the predetermined voltage boosted by the boosting circuit is applied to the drive circuit.
In this electric power steering apparatus of the sixth invention, the torque sensor detects the steering torque applied to the steering wheel, and the steering assisting motor is driven by the drive circuit to which the voltage of the mounted battery is applied. The motor current instruction value representative of the value of the current to be flown through the motor is determined based on the steering torque detected by the torque sensor, the drive circuit rotates the motor based on the determined motor current instruction value, and the steering power is assisted by the rotation torque outputted by the motor. The rotation number detector detects the number of rotations of the motor, and the judging means judges whether the number of rotations detected by the rotation number detector is higher than the first threshold value or not. When the judging means judges that the number of rotations is higher, the boosting instruction outputting means outputs the boosting instruction for boosting the voltage of the mounted battery to the predetermined voltage in accordance with the number of rotations detected by the rotation number detector. The boosting circuit boosts the voltage of the mounted battery to the predetermined voltage in response to the boosting instruction outputted by the boosting instruction outputting means, and the predetermined voltage boosted by the boosting circuit is applied to the drive circuit.
According to this structure, the voltage of the mounted battery can be boosted in accordance with the number of rotations of the motor, and a voltage from which a stable steering assisting force is always obtained can be supplied to the steering assisting motor even when the voltage of the mounted battery falls, so that an electric power steering apparatus in which the steering assisting motor has a reduced size is realized.
An electric power steering apparatus according to a seventh invention is characterized by further comprising in addition to the sixth invention: first judging means for judging whether or not the number of rotations detected by the rotation number detector is lower than a second threshold value that is lower than the first threshold value during the boosting circuit boosts the voltage of the mounted battery to the predetermined voltage; and stepping down instruction outputting means for, when the first judging means judges that the number of rotations is lower, outputting a stepping down instruction for stepping down the voltage, wherein the boosting circuit stops the boosting of the voltage of the mounted battery to the predetermined voltage in response to the stepping down instruction outputted by the stepping down instruction outputting means.
In this electric power steering apparatus of the seventh invention, during the boosting circuit boosts the voltage of the mounted battery to the predetermined voltage, the first judging means judges whether or not the number of rotations detected by the rotation number detector is lower than the second threshold value that is lower than the first threshold value. When the first judging means judges that the number of rotations is lower, the stepping down instruction outputting means outputs the stepping down instruction for stepping down the voltage, and the boosting circuit stops the boosting of the voltage of the mounted battery to the predetermined voltage in response to the stepping down instruction outputted by the stepping down instruction outputting means.
According to this structure, when it becomes unnecessary to boost the voltage of the mounted battery applied to the drive circuit, the boosted voltage of the mounted battery can be stepped down, and when a large steering assisting force becomes unnecessary, the voltage of the mounted battery can be supplied to the steering assisting motor without boosted, so that an electric power steering apparatus is realized in which the efficiency of the steering assisting motor can be prevented from being reduced by the boosting of the voltage of the mounted battery.
An electric power steering apparatus according to an eighth invention is characterized by further comprising in addition to the sixth or seventh invention: judging means for judging whether the motor current instruction value is higher than a third threshold value or not; and calculating means for calculating the rotation torque when the judging means judges that the motor current instruction value is higher, wherein the boosting instruction outputting means outputs a boosting instruction for boosting the voltage of the mounted battery to the predetermined voltage in accordance with the rotation torque calculated by the calculating means and the number of rotations, and the boosting circuit boosts the voltage of the mounted battery to the predetermined voltage in response to the boosting instruction outputted by the boosting instruction outputting means.
In this electric power steering apparatus of the eighth invention, the judging means judges whether the motor current instruction value is higher than the third threshold value or not, and when the judging means judges that the motor current instruction value is higher, the calculating means calculates the rotation torque. The boosting instruction outputting means outputs the boosting instruction for boosting the voltage of the mounted battery to the predetermined voltage in accordance with the rotation torque calculated by the calculating means and the number of rotations detected by the rotation number detector, and the boosting circuit boosts the voltage of the mounted battery to the predetermined voltage in response to the boosting instruction outputted by the boosting instruction outputting means.
According to this structure, the voltage of the mounted battery can be boosted in accordance with the rotation torque of the motor and the number of rotations of the motor when the motor current instruction value is maximum, and a voltage from which a stable steering assisting force is always obtained can be supplied to the steering assisting motor even when the voltage of the mounted battery falls, so that an electric power steering apparatus in which the steering assisting motor has a reduced size is realized.
An electric power steering apparatus according to a ninth invention is characterized by further comprising in addition to the seventh or eighth invention: second judging means for judging whether or not the motor current instruction value is lower than a fourth threshold value that is lower than the third threshold value during the boosting circuit boosts the voltage of the mounted battery to the predetermined voltage, wherein the stepping down instruction outputting means outputs a stepping down instruction for stepping down the predetermined voltage to the voltage of the mounted battery based on results of the judgements by the second judging means and the first judging means.
In this electric power steering apparatus of the ninth invention, during the boosting circuit boosts the voltage of the mounted battery to the predetermined voltage, the second judging means judges whether or not the motor current instruction value is lower than the fourth threshold value that is lower than the third threshold value, and the stepping down instruction outputting means outputs the stepping down instruction for stepping down the predetermined voltage to the voltage of the mounted battery based on the results of the judgements by the second judging means and the first judging means.
According to this structure, when it becomes unnecessary to boost the voltage of the mounted battery applied to the drive circuit, the boosted voltage of the mounted battery can be stepped down, and when a large steering assisting force becomes unnecessary, the voltage of the mounted battery can be supplied to the steering assisting motor without boosted, so that an electric power steering apparatus is realized in which the efficiency of the steering assisting motor can be prevented from being reduced by the boosting of the voltage of the mounted battery.
An electric power steering apparatus according to a tenth invention is characterized, in any one of the first through ninth invention, in that the boosting circuit has a chopper that is actuated by the boosting instruction.
In this electric power steering apparatus of the tenth invention, since the boosting circuit has the chopper that is actuated by the boosting instruction, by the boosting circuit of a simple structure, a voltage from which a stable steering assisting force is always obtained can be supplied to the steering assisting motor even when the voltage of the mounted battery falls, so that an electric power steering apparatus in which the steering assisting motor has a reduced size is realized.
An electric power steering apparatus according to an eleventh invention is characterized, in any one of the first through tenth invention, in that the motor current instruction value is a duty ratio for PWM-controlling the motor, and the drive circuit rotates the motor through the PWM control based on the duty ratio.
In this electric power steering apparatus of the eleventh invention, since the motor current instruction value is the duty ratio for PWM-controlling the motor and the drive circuit rotates the motor through the PWM control based on the duty ratio, a voltage from which a stable steering assisting force is always obtained can be supplied to the steering assisting motor even when the voltage of the mounted battery falls, so that an electric power steering apparatus in which the steering assisting motor has a reduced size is realized.
An electric power steering apparatus according to a twelfth invention is characterized by, in addition to the tenth invention, further comprising detecting means for detecting voltage applied to the drive circuit; and PWM controlling means for controlling operation of the boosting circuit based on detected value by the detecting means so as to keep the boosting voltage constant.
According to this structure, an electric power steering apparatus can be realized in which a voltage from which a stable steering assisting force is always obtained can be supplied to the steering assisting motor even when the voltage of the mounted battery fluctuates, the size of the steering assisting motor can be further reduced.
An electric power steering apparatus according to a thirteenth invention is characterized by, in addition to the tenth invention, further comprising detecting means for detecting voltage applied to the drive circuit; and PFM controlling means for controlling operation of the boosting circuit by varying operation frequency based on detected value by the detecting means so as to keep the boosting voltage constant.
In this electric power steering apparatus, the mounted battery is boosted by varying the operation frequency of the boosting circuit by the PFM circuit in order to reduce influence of noise by the boosting circuit when the boosting instruction is outputted.
In the PFM control, duty ration control is executed by varying number of pulses (pulse density; pulse width is constant) within constant time period, and boosting quantity of the voltage of the boosting chopper circuit is controlled by the duty ratio. At boosting, the voltage applied to the drive circuit is detected, and the duty ratio is controlled so as to keep the voltage applied to the drive circuit constant.
According to this structure, an electric power steering apparatus can be realized in which a voltage from which a stable steering assisting force is always obtained can be supplied to the steering assisting motor even when the voltage of the mounted battery fluctuates, the size of the steering assisting motor can be further reduced, and the electromagnetic noises caused by the boosting chopper circuit are converted into white noises, so that the influence of the electromagnetic noises can be reduced.
An electric power steering apparatus according to a fourteenth invention being provided with: a torque sensor for detecting a steering torque applied to a steering wheel; and a steering assisting motor driven by a drive circuit to which a voltage of a mounted battery is applied, in which a motor current instruction value representative of a value of a current to be flown through the motor is determined based on the steering torque detected by the torque sensor, the drive circuit rotates the motor in accordance with the determined motor current instruction value, and a steering power is assisted by a rotation torque outputted by the motor, the electric power steering apparatus being characterized by composing: judging means for judging whether an output of the motor is insufficient or not; boosting instruction outputting means for, when the judging means judges that the output of the motor is insufficient, outputting a boosting instruction for boosting the voltage of the mounted battery; a boosting circuit for boosting the voltage of the mounted battery in response to the boosting instruction outputted by the boosting instruction outputting means; detecting means for detecting that a voltage applied to the drive circuit becomes higher than a predetermined voltage; and a switching element for connecting the drive circuit and the mounted battery when the detecting means detects that the voltage applied to the drive circuit becomes higher than the predetermined voltage, wherein when the voltage applied to the drive circuit becomes higher than the predetermined voltage, a current is fed back from the drive circuit to the mounted battery.
In this electric power steering apparatus, the torque sensor detects the steering torque applied to the steering wheel, and the steering assisting motor is driven by the drive circuit to which the voltage outputted by the mounted battery is applied. The motor current instruction value representative of the value of the current to be flown through the motor is determined based on the steering torque detected by the torque sensor, and the drive circuit rotates the motor based on the determined motor current instruction value. The judging means judges whether the output of the motor is insufficient or not. When the judging means judges that the output of the motor is insufficient, the boosting instruction outputting means outputs the boosting instruction for boosting the output voltage of the mounted battery. In response to the output boosting instruction, the boosting circuit boosts the output voltage of the mounted battery. The detecting means detects that the voltage applied to the drive circuit becomes higher than the predetermined voltage, and when the detecting means detects that the voltage becomes higher than the predetermined voltage, the switching element connects the drive circuit and the mounted battery. When the voltage applied to the drive circuit is higher than the predetermined voltage, a current is fed back from the drive circuit to the mounted battery.
According to this structure, an electric power steering apparatus can be realized in which a voltage from which a stable steering assisting force is always obtained can be supplied to the steering assisting motor even when the output voltage of the mounted battery fluctuates, the size of the steering assisting motor can be further reduced, and the motor and its drive circuit are never damaged by the electric power generated by the motor.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.